Other than a trip which might get the odd mention I will detail projects I am working on, what I want to be working on and what I have otherwise to report on.
I will update the individual projects as they advance.
As asked I have started to catalogue the references I have follow the link on the left where you can obtain them too. Want to email me wander over to qrz.com and you'll find my email address there. Also twitter @m1kta_qrp

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Tuesday, 30 March 2010

If you have worked with USB at all you might know that if you build a device with a USB interface you will quickly discover one of the requirements of the USB device/interface is to be able to identify itself so M$ OS (or some other) can load the appropriate driver to get it to work, so you can send and receive data through it. If you are just building something for yourself at home and will never share it with others you can pretty much select almost anything, as long as it does not conflict with something else you own (which is what I had done so far). To do this and to share the design with others though is a tad more complicated, and expensive, you need to obtain a unique VID/PID combination for your carefully crafted bit of homebrew. The two parts VID and PID the first VID identifies who you are, or rather who the seller of the USB device is, the second identifies the 'product', so you can imagine someone selling a range of USB widgets would have one VID and a range of PID to identify each product. Simple enough to understand :-)

Now somewhat niavely I thought Ok I better go and get a VID and PID.... then the reality hit me. Far from simple and certainly not cheap.

The VID, is a 16-bit value that identifies who the manufacturer of a USB device is, and there is a lookup table (www.usb.org).

The PID, would then identify which product manufactured by the vendor, or more usually which driver that device might use .

Then the combination of the VID and PID should provide a unique reference to the driver required for each and every USB product on the market.

In addition to the VID/PID combination there is another number that can be added (I think some products use these to identify for licence keys etc.) so every device in a VID/PID pair could have a unique serial number. So for example say a range of SDR you would have one type of USB/SDR and each has a different serial number.

So far still easy to understand...

So try and get a VID/PID and note the costs involved or the legal garbage you get handed! Eek they must be joking, but they are not, and if you only want a couple (at most I suspect even kit makers will only ever use a dozen or so) it makes no difference, so there is the conundrum...

Right now trying to work out for myself which way I am going to go... Use V-USB, Microchip or FTDI or even obtain a VID outsight!

How's this radio?

Well I'm working with Simon Brown HB9DRV on SDR-Radio.com as well as my own designs for usb controlled kit and this now a problem.

It is a bit like if you are running you own network at home you happily use IP's from 192.168.1.x or whatever to identify your PC and 1,000's of others, companies too, do the same thing but go outside your home/company and all those websites have their own IP.

Years ago the IP subnet 44.x.x.x was grabbed for amateur radio. The class A 44 netblock of 16.7 Million IP addresses was set aside for amateur radio users worldwide, having been secured in the 1970s by Hank Magnuski, when the internet was in its infancy. Shame the same never happened for USB devices.

Sunday, 28 March 2010

I will be helping Simon with some of the technical /hardware aspects of the useof Softrocks, and I mean those with static and Si570 LO so V6.2 Lite RX, V6.3RXTX and V9.0 RX versions initially with the SDR-Radio software on differentplatforms (there will never be a Linux version of SDR-Radio - It is better towrite a piece of software that works well on one operating sustem that averageor not at all on many). To save time and answering questions about it more thanonce please do not expect TX support in the current releases as it will not beavailable until end of May 2010 at the earliest.

72

DomM1KTA

--- In softrock40@yahoogroups.com, "Simon HB9DRV" wrote:>> Hi All,>>>> Together with M1KTA I'm getting ready to make a sdr-radio.com kit with USB> support. To help me avoid as many errors as possible, I would like> information shown using PE0FKO's configuration utility.>>>> If you have this from http://home.ict.nl/~fredkrom/pe0fko/CFGSR/ I would> like to know the information shown on the first page:>>>> Manufacturer: www.obdev.at>> Product: DG8SAW-I2C>> Serial number: PE0FKO-2.0>>>> Hoping for a kit on Sunday if you're good :)>>>> Simon Brown begin_of_the_skype_highlightingend_of_the_skype_highlighting, HB9DRV>> http://sdr-radio.com

The USB driver, and then any SDR software, whatever is being used should be looking for some things to identify a USB device and the Firmware on the AVR in a Softrock will also provide these....

In the AVR code the sections are;

#define USB_CFG_VENDOR_ID 0xc0, 0x16 /* 5824 in dec, stands for VOTI *//* USB vendor ID for the device, low byte first. If you have registered your* own Vendor ID, define it here. Otherwise you use obdev's free shared* VID/PID pair. Be sure to read USBID-License.txt for rules!*/#define USB_CFG_DEVICE_ID 0xdc, 0x05 /* 1500 in dec, obdev's free PID *//* This is the ID of the product, low byte first. It is interpreted in the* scope of the vendor ID. If you have registered your own VID with usb.org* or if you have licensed a PID from somebody else, define it here. Otherwise* you use obdev's free shared VID/PID pair. Be sure to read the rules in* USBID-License.txt!*/#define USB_CFG_DEVICE_VERSION 0x00, 0x01/* Version number of the device: Minor number first, then major number.*/#define USB_CFG_VENDOR_NAME 'w', 'w', 'w', '.', 'o', 'b', 'd', 'e', 'v', '.', 'a', 't'#define USB_CFG_VENDOR_NAME_LEN 12/* These two values define the vendor name returned by the USB device. The name* must be given as a list of characters under single quotes. The characters* are interpreted as Unicode (UTF-16) entities.* If you don't want a vendor name string, undefine these macros.* ALWAYS define a vendor name containing your Internet domain name if you use* obdev's free shared VID/PID pair. See the file USBID-License.txt for* details.*/#define USB_CFG_DEVICE_NAME 'D', 'G', '8', 'S', 'A', 'Q', '-', 'I', '2', 'C'#define USB_CFG_DEVICE_NAME_LEN 10/* Same as above for the device name. If you don't want a device name, undefine* the macros. See the file USBID-License.txt before you assign a name.*/#define USB_CFG_SERIAL_NUMBER 'B', 'e', 't', 'a', '1', '.', '1'#define USB_CFG_SERIAL_NUMBER_LEN 7/* Same as above for the serial number. If you don't want a serial number,* undefine the macros.* It may be useful to provide the serial number through other means than at* compile time. See the section about descriptor properties below for how* to fine tune control over USB descriptors such as the string descriptor* for the serial number.*/#define USB_CFG_DEVICE_CLASS 0xff#define USB_CFG_DEVICE_SUBCLASS 0/* See USB specification if you want to conform to an existing device class.*/#define USB_CFG_INTERFACE_CLASS 0#define USB_CFG_INTERFACE_SUBCLASS 0#define USB_CFG_INTERFACE_PROTOCOL 0/* See USB specification if you want to conform to an existing device class or* protocol.*/#define USB_CFG_HID_REPORT_DESCRIPTOR_LENGTH 0 /* total length of report descriptor *//* Define this to the length of the HID report descriptor, if you implement* an HID device. Otherwise don't define it or define it to 0.

So anyone that writes software for a Softrock you MUST know what these are.

Now if any SDR software looks at the USB devices and needs to match these before working then all three need to be correct. Obviously you might be able to separately identify each Softrock if you had more than on (and were able to recode your AVR).

What Simon (HB9DRV) was looking for was these three lines the USB/AVR chip would return.

I will be working to make sure we know which versions work and those that don't.

Please don't bombard me with comments about your version being different at this point or claim this will mean SDR-Radio will not work with softrocks.... it will. I say this because I'm doing the SDR-Radio softrock support and I asked for support for Softrocks to be included!Simon will just use the VID/PID to identify which USB device is being used. The Softrocks tend to all have the VID/PID using the licenced V-USB VID/PID from obdev right now but there are others than have used different details, as PE0FKO usb/AVR code has been hacked/rewritten by some so that their details are different, some will be official, some not (and I fall into the second category as I used a VID/PID combination that worked, different to obdev but is not able to be used outside my shack incase it 'clashes' with a 'real' USB VID/PID.

Sunday, 21 March 2010

The empty PCB of the new TRX, note the isolation of the USB/Si570 from the RF on TRX board

The build process loosely follows (photos and details to be inserted):

Inventory the kitBuild and test the 12, 5 and 3.3 Vdc power suppliesBuild and test the USBBuild and test the Si570 Local OscillatorBuild and test the IsolationBuild and test the DividersBuild and test the RX OpAmpsBuild and test the RX Mixer(QSD)Build and test the RX BPF(s) (L4);Build and test the TX OpAmpsBuild and test the TX Mixer (QSE)Build and test the PTT circuitsBuild and test the RX Switching circuitsBuild and test the PA/Filter(s) (L2/L3)Install the External Connectors (those not be placed before anyway)

Saturday, 20 March 2010

OK so I have a Laptop or PC, Softrock SDR hardware and an antenna what next...???

This post is a place holder for me really.

The latest series of SDR Softrocks use Si570 USB control and I've been asked to document exactly what is required for someone starting off from a new laptop or PC and they have either built their own Softrock (V6.3 TRX or V9.0 RX) or got someone else to build it for them (I do build these for others in nice die cast boxes) but puzzled what they have to do next.

Also the non Si570/USB fixed frequency SDR Softrocks there are loads of those out there and I will document these too.

I'll blog the steps here (they will probably also appear else where too).

This will not involve any radio theory and will not be details about what to solder what where as there is loads of that advise already out there, it will just be about how to get the SDR software working with the hardware.

Saturday, 13 March 2010

Well the loss of the tall supports didn't stop me (M1KTA) entering RSGB BERU contest as strung up a low (centre 20ft AGL) inverted V dipole for 40m and 10m.

And managed some qso on 15m :-) none on 10m though.

So far it's 7pm and went qrt at 5:30pm to make some food and even though took over a hour at lunch too I have almost hit the same qso score as last year and in less than half the time! Dropped the qrp though as was getting no responses with the low antenna and it wasn't until reached 20W that any VE's responded (but not very efficiently).Got a couple VK's in the log already too!

Thanks Bob G3PJT for, a while ago now, the cw coaching and showing me how to use win-test!

As just a 12 hour entry I think I'll probably do one more hour tonight and then get up at 3am for the grey line/morning openings on 80m and 40m tomorrow and I'll turn the dipole into a long wire for that.

Sterba curtain broke the antenna supports so had to sling a really low dipole up apex at maybe 16ft agl although should be 20ft but centre doesn't go to top of pole. No responses with 5W despite trying and G4EAG finally said just audible above noise after increasing to below 20W so abandoned qrp and will remain at just under 20W but I suspect that has more to do with the antenna! Anyway I'll be a non-QRP entry this year. And I tracked down GB5CC too!

Loads of stations heard on 15m this year :-)

Just finished first stint and 61 contacts

As was using Softrock SDR V9.0 RX and SDR-Radio.com software could 'see' the activity before tuned to it. The new Af filters meant at time was using 50Hz filters so the signals were wonderfully clear.

Friday, 12 March 2010

Rats... was looking good then one of the end supports just failed terminally when I tried to tension and now it tops out at only 20ft AGL. I don't think bottom at 3 feet AGL will work!

Raining so off indoors for tea and and rethink. Maybe could use three 10m fishing poles to support the antenna between the phasing lines? Obviously too much weight to hope two will support the lot as they are too bendy. This is after all only temporary.

Maybe a price of £159 for the 4 TV poles and guys wasn't too bad after all!

One email has suggested....

Another cheapo way to make masts is to use white plastic waste pipe with ex 2"x2" timber inside them. You will have to plane the edges to slide the wood in but this way you can create a fit-together sectional mast. It will need guying though.

...so that might be part of a 'cunning plan' as Baldric would have said.

I could have died as just got the curtain up when the far supportjust bent over. Made from sections of Ali pole riveted together andsplit and bent in the middle of one section where no join existed!Wasn't slow motion but felt like I was watching a disaster unfold butfortunately missed the green house! Important bit is the antenna andfeeder are fine.

2009 BERU I made ZERO contacts on 15m and 10m and this year intend tomake at least one on both bands ! Although coming last 2008 doesn't botherme I get ribbed about it a bit so about time I did better!

Admitting defeat with the Sterba Curtain as I cannot get the supports high enough and wet right through now. I need the bottom wires to be min 16 feet AGL which means top at 35ft+ and just cannot manage more than 25ft. I just don't have the supports that will 'launch it higher'. Should have bought the TV poles and built a one off pair of 40ft supports so back to low dipoles on 15m and 10m this w/e but means in the restricted not the open category.... still think as much chance of a QRP qso as the sun being full of sunspots.

From GQRP list....On 11 March 2010 18:46, Richard Constantine wrote:> Hows About a picture of it Dom? Should really up your erp.> Richard G3UGF

So here is the blog post.

Hi Richard,

When it is up I will post to blog photos and the build bits too.

The design was lifted right out of the ARRL Wire Antenna Classics and is by K1TN from QST, October 1991, Chapter 6 (6-9)

The first thing to do was to make up the top section and make sure I could suspend it in the clear, I used string as the horizontal sections and will suspend the antenna from it. Using light weight multistrand PVC coated wire so the lengths might be out slightly compared to 14SWG and originally was going to use some dog bones for connectors but cable ties are much lighter in weight. Also will cable tie the horizontal sections loosely to the support string.

One modification though, I'll be feeding dead centre at the bottom of the centre section and probably using 300ohm (run out of 450 ohm!) . I was trying to find some 40 foot supports yesterday, doubled up 20foot long thick walled TV masts with coupler and end guys seem to be the best option, as the antenna sags a little. I will be 'supporting it' with some telescoping fishing poles to push the middle up a bit so will not be all square so the radiation pattern might be interesting.

As some might know my QTH there are two lovely 70 foot poplars in neighbours garden to East with 100 foot separation between them but alas cannot use them as supports!

Thursday, 11 March 2010

OK first things first... public apology to Tony as I hit post not save as this should have waited a while but Tony has said fine to blog this and my build.

The Ensemble combines the V6.3 RXTX, PA/Filter kit and USB Interface on a single 2.5 by 5.0 inch circuit board. The USB interface and USB powered Si570 are opto and transformer isolated from the rest of the RXTX circuits and results in almost no USB noise on the RX function. He has included board mounted connectors along one edge of the board making it convenient to mount the board within a metal box. The builder would select a band group, (160m, 80m/40m, 30m/20m/17m, or 15m/12m/10m), at the time of building the kit.

I will have completed a build and this will be on air at the SHARE rally 11th April near Inneskillen North Ireland where I will have a homebrew display and will also be running Simon Browns SDR-RADIO software with this and other SDR projects. If you have a homebrew SDR project bring it along and lets try it out on air.

For those that also like to lay hands on kits before deciding to buy or not I will also have a pair of V6.3 TXRX and V9.0 RX kits I will have built up and a pair as basic kits.

Tuesday, 9 March 2010

> Sent: Tuesday, March 09, 2010 10:39 AM> Subject: SDR at CDARC Rally> Just wondering if you could let me know which model> Softrock kit it was that you had at the G-QRP stand at the> CDARC rally at Wood> Green this past weekend?>> best regards> Lawrence M0LCM

Lawrence,

The setup was mine....

KB9YIG Softrock V9.0 Lite with manual 80/40m LPF with V1.4 (V.OLD!) usb control software for the Si570 CMOS DDS. Would have to check but I think the op amps following the LO dividers were from the old design too not the current ones. (Just checked they are TLV2462CD not LT6231CS8)

The rig was a kit built into a simple Ali enclosure (Maplin) with telfon isolated RF-BNC (Maplin) and isolated AF phono sockets (Maplin) and power was from a 1.3AH 12V battery (Maplin) note no mains derived DC used.

Audio was double isolated using back to back 600 ohm isolation transformers with good audio response 100Hz to 25kHz (only way to find out which ones work is to test them!). As stereo means there were 4 of these transformers in the isolation interface.

Sound card is external USB 24 bit 96kHz sample rate. The sound card A/D bit number IS CRITICAL for decent SDR performance also you MUST have REAL stereo input into dual A/D channels (only way to check is to trace the audio in on the M/B and locate the chipset and do some data sheet look ups. It really does make a difference. Normal PC cards even the fancy games ones are still only 16 bit and 48Khz and MONO input.

All laptop to external connectors had common mode chokes with at least 10 turns through type -61 or -77 ferrite rings.

I demo'd SDR at CDARC rally at w/e and mentioned using an SDR Rx with an old TX and was posed this question by email just now:

> Hello> Dominic,>> I'm sure that you had thousands of discussions with people at the Wood Green Rally on Sunday;> however, you were telling me that you were planning to use a SoftRock SDR (possibly)> receiver with a valve transmitter for contests, etc.>> How are you planning to get the tx on the same frequency? Just by frequency meter?

This was my response:

Hi ,

If using a valve TX then usually you know the TX frequency in advance. Especially (mine is) if xtal controlled, so you cannot usually tell the other station the freq so hope they are playing nicely and they move their RX to it. If VFO based you will have to match your TX to their RX, unless you are the run station.

I listen for the remote station using SDR RX that is frequency agile, and TX on the 6V6. I am the run station so I do not move the TX frequency and to some degree don't really care what it it as long as stable, in band etc... As per most xtal based qso the frequencies are well known and established 3.560, 3.558 or 3.579 are three that many know and use. G3VTT recently sent me a whole bag full of FT243 80 xtals so I have the ability to cover 3.500 to 3.600 almost every 15kHz or so. Xtal based TX are limited and only on fixed frequency so if you have DX or contest operators that don't work with you then you will have trouble.

However, if my TX were a homebrew frequency agile (VFO) then I'd use a frequency counter to confirm my TX freq. If I were using a commercial valve TX then I can usually read the TX frequency off a dial or whatever.

Most contests are simplex so Rx freq = Tx freq. Some using valve TX as sure you know will allow Rx VFO to help cope with the Tx limitations of fixed frequency operations.

The method all depends on if you are 'run' or 'search and pounce'. If I were HB0/M1KTA or even 3B8/M1KTA again I don't think it would matter what the Tx freq was hihi..

No circuits provided at this stage but I will provide the component counts in [ ] brackets.My ideas are:TX VXO with a small amount of possible variation using a variable capacitor.RX would cover a small mybe 20kHz section using a variable capacitor .

TX is a simple vxo mosfet (IRF510 or RD06HHF1) in a colpitts layout [+12] with a minimal lpf [+3] that does double duty as the RX signal goes through the TX lpf. Some XIT is possible as I used a small variable capacitor in series with the the xtal on the ground leg side, if no XIT wanted could remove one component. TX muting is accomplished using a keying circuit and I used a mosfet (2N7000) as the RX mute [+4], turning off he RX feed I would have liked to extend this into the AF chain too as there is a bit of a 'thump' in the audio on change over and I had thought to add a filter but already note component count on RX is high. Test showed 3W out possible from SLA at 12V. No side tone but would make operating for me easier if I used a simple piezo sounder attached to the key/mute circuit [+1]. TX = [20]

RX seemed to use way too many components and thought this is impossible as I originally started off with a typical BPF [+8] but then realised I had some TOKO coils [+5] then I noted if paid a bit more attention to using the TX LPF and used my MiniVNA and looked carefully at the filter characteristics I could manage to build a high pass filter which in addition to the TX lpf makes up the RX bpf. It is possible to strip the RX filter down to a single TOKO coil and one cap [+3]. Then as this cannot be a DC RX the Rx requires a VFO either a colpitts or pierce, fixed [9] if using VXO [+11], LC [+11] or varicap [+12]. Anyway this then feeds into the IF chain, for a mixer there are a lot of ways to do this and usually a 602/xtal/602/lm358 would be employed but given the IC count is one and I want to use this in the AF (LM386) and either a switch IC 4066 or 74HC4053 cannot be used as they don't count as switches but with [32] and [64] components respectively the option of a DBM [+6] at each end was the first option tried. Now these could either be SBL-1 or similar or FT37-43 and 4 matched 1n4148's I chose the latter. However I looked at other options, using one a transistor (2N2222A) as a mixer [+9], use of a dual gate fet (bf998) [+5], a fet (J310) and PNP (2N39906) [+6]. The detector uses the same configuration as the mixer [+5 to +9], but you could make use of a dual gate fet (bf998) or a fet (j310) and PNP (2N3906) or NPN 2N2222A in a configuration (similar to that which DL6CGC used in the MASter80) where the upper part of the dual gate mosfet acts as the BFO [+9 minimal]. Or you use a separate BFO [detector +9]. The Crystal filter could be made with just a single crystal and two caps [+3] but you have to match the BFO and the one used in the filter closely. For the AF I used my one IC (LM386) [+4] into headphones.RX = [37 best case].

The power regulation LM7806 or LM7806 uses [+4] or use two battery packs one for 6/8V one for 12V [0]. I would add a reverse protection diode [+1]Power = [5]

Anyway I was invited by Michael Clarke MI5MTC to visit with a home brew display (similar to GQRP Rishworth) and I will also take a collection of the latest SDR home brew radio kits you can obtain (I am a beta builder for a couple of kit suppliers) along with the latest software from Simon HB9DRV, he wrote Ham Radio Deluxe you might know already.

I plan to have built and kit versions of a couple of the SDR radios for sale with me (I will not sell over the internet) and as Simon will have added support for the Softrock SDR (Si570 USB) just the week or so before hand this might be the first opportunity many will have to see it running live.

Hopefully in time for the rally I am already prototyping a little interface (all suggestions welcome) that will allow one of these SDR RX to be added into an old TXRX (or just TX) even valve radio like my own 6V6 TX.

The E licence has not arrived yet but will be qrv in Ireland on the trip as driving from Cambridge and will be on the ferry to Dublin and hoping to do a loop through all the counties of Ireland. (Yes know could be E/M1KTA/P as well as CEPT allowed)

I have decided to stop selling off project builds now and I am keeping hold of everything until a rally when I can sell them in person as I have had a complete nightmare after selling one of the projects over the internet to someone I believed was capable of finishing it and has demanded I rebuild and re-align it after they hacked about with it themselves to the point where it no longer functions, they melted the pcb connectors and filed away part of the pcb and at least one track in the process to attempt to squeeze it into a box that was too small and demanded a paypal refund.

I do not have the money or the time to repair and realign projects I had already built so for now I am never again selling a 'built' project over the internet it is too risky for me.

Sunday, 7 March 2010

Ran a GQRP stall at the CDARC rally with Clive (M5CHH) and ran a demo of Simon (HB9DRV) SDR software with a Softrock V9.0 by Tony Parks (KB9YIG) and used a W3EDP antenna. Plenty of interest and was kept busy all rally long. Should have had some kits available for sale... note to myself for next time.

Adding the laptop, external speakers, sdr radio and antenna made many stop and take a close look. It was fun trying to explain to small groups how sdr worked and how once the signal is digitised there are all sorts of things that can be done with it. Several said thought I was cheating some how when showed them the actual SDR hardware! To be fair I also showed M0KGK and Rocky SDR software side by side with Simon's new software a couple times but most stated there was no comparison between them. Having a wonderful AF spectrum filter display I took an extra flat panel and attached it to the laptop and showed how the filtering worked.

Live demos are always a bit risky but as if by magic several stations were fighting over a DX contact in a cw pile up which gave a perfect opportunity to show filtering down to 50Hz (yes fifty not 500Hz) and there was a contest on and picked out many US stations on 40m and again showed the filtering to sub 1.7KHz being able to separate the SSB signals easily... now that wowed more than a few. Positive we had a radio vendor over at one point observing.

We sold out of all the SPRAT CD's and the Drew Diamond books we took along.

Many thanks for the support from GQRP members that came and said hello.

For those that asked today please get in touch about building the Softrock and setup help.

Clive's note:

The rally was a great success. Dom brought along a 40 M SDR front end with Simon Brown's latest SDR (Beta) software he is testing. I rigged a W3EDP antenna with a hb tuner to feed it. That certainly gathered a crowd. He also brought along his XYL Christine who was the star of the GQRP stand. Essentially we (she) sold all the Drew Diamond books, all the SPRAT 1-140 CDs and all but two of the M0JRQ antenna books. Christine did most of the sales in the first couple of hours.

It just goes to show that a pretty woman on the stand beats an Old Fart any day. We were pre-charged £15 for the table just the same as any other trader, so Dom brought along some of his junk and could have sold several SDR kits had we known.

Tuesday, 2 March 2010

I have started to put the observatory together again and find i need to create a dew heater and controller for the LX90 8" SCT telescope at M1KTA. After some googling I came up with a couple of options and I like one from Don Clements, I had a look in the junk box (!!) and found I had some LM355 temperature sensors.

So decided to attempting to build a circuit that will provide automatic control of a heater element (made from simple resistors, soldered into a ring and then covered in shrink wrap) that will surround the telescope optics. These optics maybe any of the secondary mirror, primary, eyepieces, or the telrad finder. The concept is for the circuit to automatically maintain the temperature of the optics, at a few degrees (preset) above the ambient air temperature, so dew does not form on the optics.

The initial idea is the temperature is measured using LM335 precision temperature sensor that output 10mV/degree K. There are two one measures the ambient temperature, the other the temperature as close to the optics as possible by the heaters. I will call these tempsense1 and tempsense2 and these have a small bias applied to them, these voltages are fed into an opamp in a simple comparator configuration so that a small difference is amplified and this is output such that it can drive the gate of a switching MOSFET. If the two temperatures are close then there is no voltage difference so the MOSFET is turned off, if there is a difference the MOSFET is switched on, what is switched is the current that goes through the heater.

In the telescope configuration most likely to be used there are four potential heaters so the circuit is replicated three times.

One important calculation that needs to be done is detailed here. You need to determine the resistance of the heater used and the following equation is used: where V=battery voltage, Rdh=resistance of dew heater, Rmosfet=drain to source resistance of the MOSFET used, P= power dissipation of heater

So lets assume one wants 12W heater and V=12V and Rmosfet=0.5 ohm then Rdh= 11 ohms The actual heater size will have to be determined by the size of the optics. In my case I have an approximate 9" tube for the secondary, same for the primary and two 3" heaters, one for the finder scope and the other for the eyepiece.

If all 4 are 12W (bit high) the current needs are simple to calculate using I=W/V or 12/12 or 1amp per heater.

Operating location from a top in alps c2600m

Now this was a perfect SOTA location, I stayed on top overnight and used the flag pole to my right to support a 40m/20m dipole, you can see the fixture I connected to, the little ring clamp, as soon as the cable car stopped for the night out came the radio gear, it even snowed! If I had taken 2m yagi would have been amazing location as line of sight was > 80miles, the Eiger and Jungfau (Bernese Oberland group) are in the photo over my right shoulder. Temp dropped to below minus 15 but the morning operating the grey line was fun 100 or so QSO SSB qrp as HB9/M1KTA/P.